Study of the CaF2/Si interface using x-ray photoelectron spectroscopy

Abstract

The interfacial properties of CaF2 on Si(111) under two different deposition conditions are studied using x-ray photoelectron spectroscopy (XPS). The CaF2/Si sample grown at a fixed temperature of 600 °C exhibits B-type epitaxy. For the second sample, the Si substrate was ramped from 100 to 600 °C in 5 min and then held at 600 °C until the end of the deposition. Under these conditions, the film exhibits A-type epitaxy, with very different electrical properties. The XPS analysis shows that for both samples, Si is bonded with both Ca and F at the interface. Significant differences are observed, however, for the chemical environment of Ca in the interfacial region for the two samples. In the first sample, Ca–Si bonding is relatively more pronounced, while in the second sample Ca–O bonding is observed to be predominant. In addition, for the sample grown under ramped temperature conditions, the fluorine dissociation is observed to be less and more F–Si bonds form at the interface. The results of this study help to explain the widely different electrical properties of the two films.